This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Perennial. Propagates by seeds and by rootstocks. Time of bloom: May to September. Seed-time: July to November. Range: Massachusetts, Connecticut, and southern Ontario, to Iowa and Kansas, southward to Florida and Texas. Habitat: Meadows, pastures, and cultivated ground; invades all crops.
A near relative of the potato and one of the worst weeds native to this country; southern in its origin but rapidly making its way northward and westward through the agencies of impure clover seed and baled hay. The deep-seated rootstocks are most tenacious of life; an Indiana farmer states that they "will live ten years under a heap of sawdust and grow as soon as the dust is removed." Sheep are the only grazing animals that will touch the plant, and they merely nibble off the fruits; the seeds are widely scattered in their droppings and many a productive acre is thus practically ruined. (Fig. 255.)
Stem six inches to two feet tall, erect, loosely branched, roughened with short, stiff, star-shaped hairs, and beset with sharp, awl-shaped, yellow spines. Alternate leaves two to five inches in length, oblong to ovate in outline, irregularly and coarsely wavy-toothed, or sinuate-pinnatifid, covered with star-shaped hairs, veins and midrib prickly on both sides as are also the petioles. Flowers in open cymose clusters on prickly peduncles which spring from the side of the stem between the leaves, at first appearing terminal but becoming lateral as the stem lengthens; corolla pale violet or bluish white, five-lobed; stamens with anthers equal and tapering toward the summit; calyx-lobes hairy, rather short, acute, persistent at the base of the fruit, which is an orange-colored berry, smooth, globular, about three-fourths of an inch in diameter, full of juicy pulp and flattened, straw-colored seeds.
If the infestation is new and the area not too large, the plants may be killed outright by the use of hot brine, caustic soda, or kerosene which usually destroys all accompanying growths or, if pains are taken to apply the herbicide directly about the roots of the weeds, the neighboring plants may not be greatly damaged. If possible, all seed development should be prevented, which means early, deep, and frequent cutting with hoe or spud; salt on the cut surfaces will retard new growth and will also induce stock to bite off young shoots. In order to destroy the rootatocks short rotations are necessary, alternating cultivated crops, to which are given such thorough tillage that no green leaves are allowed to appear on the weeds, with such crops as rye, clover, and vetch, which will choke and smother the Nettle, supply late pasturage, and then be plowed under to furnish humus for another cultivated crop, well tilled. Two or three seasons of continuous effort are required in order to suppress the weed, but the labor is well repaid by the deliverance of the soil from such a pest.
Fig. 255. - Horse Nettle (Solarium carolinense). X 1/4.